In the copending application there is disclosed a spiral or helical brush section adapted to be used in multiples of axially-interfitting or nesting sections to complete a rotary brush of desired length. Each section is made of a relatively short split tube section or drum which has its ends offset at its joint to form contact shoulders so that the shouldered end of one section will interfit with and engage the shouldered end of the adjacent section when slipped axially on the mandrel. Each section has a brush strip helically wound thereon which consists of a channel having U-shaped bristles disposed thereon. The bristles are retained in the channel by means including a retaining wire which may be used as an aid in locking the channel to the offset end of the tube. In placing the sections on the mandrel the sections must be rotated to position them properly axially so that the adjacent sections interfit and there will be no gaps in the bristles at the adjacent ends of the bush strips of interlocking sections.